Even if Resident Evil 4 Remake doesn't end up getting the Separate Ways content as a DLC, it's likely that Capcom will announce something -related during its showcase.

Source: https://gamerant.com/capcom-showcase-expectations-exoprimal-resident-evil-dragons-dogma-2/

Namely, the 2005 original had one final bonus mode in the form of Assignment: Ada, which would theoretically be even easier to remake seeing how much shorter it was compared to Separate Ways.

Source: https://gamerant.com/resident-evil-4-remake-dlc-leaks-separate-ways-release-date/

The first real puzzle to pop up in the Separate Ways journey is in Chapter 2, when your progress is impeded by a door that can only be unlocked by pressing specific symbols on a mechanism beside it.

Source: https://www.digitaltrends.com/gaming/resident-evil-4-separate-ways-chapter-2-door/